Calls for the simplification of taxation are frequently heard but attempts to achieve actual tax simplification have rarely met with lasting success. To investigate further, the present authors asked relevant experts to report on the experience of tax simplification in Australia, Canada, China, Malaysia, New Zealand, Russia, South Africa, Thailand, Turkey, the UK and the USA. In addition to tax simplification, the country experts were asked to provide information on simplification in relation to the following aspects: tax systems, tax law, taxpayer communications, tax administration and any more fundamental approaches. Their accounts were published in a book edited by the current authors early in 2016. This paper analyses the experiences of the 11 countries and it is clear that a considerable degree of complexity is inevitable given the different aims of taxation and the complex socioeconomic environments in which tax systems have to operate. The key question is how to distinguish complexity which is necessary for the functioning of a successful tax system from that which is not. This paper focuses on the relevant factors and issues involved in classifying unavoidable and unnecessary complexity not only with respect to legislation but also tax policy and administrative systems.